Boland, 66, from Yonkers, allegedly went to St. Barnabas Church in Woodlawn, and left three letters. One, found Sunday, included the frightening line, “Those who kill you are doing a holy duty of God.”

Police discovered two more letters, one in a priest’s mailbox, and the other in a prayer book.

The three letters, referencing the prophet Muhammad and beheading nonbelievers, were found at St. Barnabas Church in Woodlawn.

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The letters talked about the Prophet Muhammad, the Gospel and beheading nonbelievers, a source said.

Boland was charged with making terrorist threats, a felony, and aggravated harassment, a misdemeanor.

But he was later released after the Bronx District Attorney declined to prosecute him.

"We certainly understand that, in the current climate, the notes were very frightening to people. However, the notes in question do not constitute a threat, but rather a severely misguided attempt to warn of potential harm done by others," the Bronx DA said in a statement.

"After an extensive review, the Bronx DA has determined that we do not have sufficient evidence by which we could prove either a threat or an intent to annoy or alarm, beyond a reasonable doubt. Mr. Boland has been advised that his future presence in St. Barnabas Church will lead to trespass charges," the statement concluded.